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		<h1>shell 练习-实现一个小型计算器</h1>
	
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		<span class="article__date">2017-10-12</span><br />
		
		
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			  	<a class="article__tag-link" href="/tags/shell练习/">shell练习</a>
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		<figure class="highlight bash"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div><div class="line">26</div><div class="line">27</div><div class="line">28</div><div class="line">29</div><div class="line">30</div><div class="line">31</div><div class="line">32</div><div class="line">33</div><div class="line">34</div><div class="line">35</div><div class="line">36</div><div class="line">37</div><div class="line">38</div><div class="line">39</div><div class="line">40</div><div class="line">41</div><div class="line">42</div><div class="line">43</div><div class="line">44</div><div class="line">45</div><div class="line">46</div><div class="line">47</div><div class="line">48</div><div class="line">49</div></pre></td><td class="code"><pre><div class="line">[root@nfs01 scripts]<span class="comment"># cat bc.sh </span></div><div class="line"><span class="meta">#!/bin/sh</span></div><div class="line"><span class="comment"># First we should save the number which was inserted by user</span></div><div class="line"><span class="built_in">read</span> -p <span class="string">"Please insert the first number and the method you want to caculate:"</span> num1</div><div class="line"><span class="built_in">read</span> -p <span class="string">"Please insert the second  number and the method you want to caculate:"</span> num2</div><div class="line"><span class="built_in">read</span> -p <span class="string">"Please insert the method you want to caculate:"</span> \opt</div><div class="line"><span class="function"><span class="title">usage</span></span>()&#123;</div><div class="line">     <span class="built_in">echo</span> <span class="string">"Usage <span class="variable">$0</span> num1 num2 operation"</span></div><div class="line">     <span class="built_in">exit</span> 1</div><div class="line">&#125;</div><div class="line"> </div><div class="line"><span class="function"><span class="title">if_int</span></span>()&#123;</div><div class="line">     num=<span class="variable">$1</span></div><div class="line">     <span class="keyword">if</span> [ ! -z $(<span class="built_in">echo</span> <span class="variable">$num</span> | sed <span class="string">'s/[0-9]//g'</span>) ];<span class="keyword">then</span></div><div class="line">           usage</div><div class="line">           <span class="built_in">exit</span> 2</div><div class="line">     <span class="keyword">fi</span></div><div class="line">&#125; </div><div class="line">if_int <span class="variable">$num1</span></div><div class="line">if_int <span class="variable">$num2</span></div><div class="line"><span class="function"><span class="title">caculate</span></span>()&#123;</div><div class="line">     <span class="built_in">echo</span> <span class="string">"<span class="variable">$&#123;num1&#125;</span><span class="variable">$&#123;opt&#125;</span><span class="variable">$&#123;num2&#125;</span>=<span class="variable">$(($&#123;num1&#125;$&#123;opt&#125;$&#123;num2&#125;)</span>)"</span>  </div><div class="line">&#125;</div><div class="line"><span class="function"><span class="title">if_zero</span></span>()&#123;</div><div class="line">     <span class="keyword">if</span> [ <span class="variable">$1</span> -eq 0 ];<span class="keyword">then</span></div><div class="line">        <span class="built_in">echo</span> <span class="string">"The dividend can't be zero,please input a number which is not equal 0"</span></div><div class="line">        <span class="built_in">exit</span> 3</div><div class="line">     <span class="keyword">fi</span></div><div class="line">&#125;</div><div class="line"> </div><div class="line"><span class="keyword">case</span> <span class="variable">$opt</span> <span class="keyword">in</span></div><div class="line">     <span class="string">"+"</span>)</div><div class="line">     caculate <span class="variable">$num1</span> <span class="variable">$num2</span> <span class="variable">$opt</span></div><div class="line">     ;;</div><div class="line">     <span class="string">"-"</span>)</div><div class="line">     caculate <span class="variable">$num1</span> <span class="variable">$num2</span> <span class="variable">$opt</span></div><div class="line">     ;;</div><div class="line">     <span class="string">"*"</span>)</div><div class="line">     caculate <span class="variable">$num1</span> <span class="variable">$num2</span> <span class="variable">$opt</span></div><div class="line">     ;;</div><div class="line">     <span class="string">"/"</span>)</div><div class="line">     if_zero <span class="variable">$num2</span></div><div class="line">     result=$(<span class="built_in">echo</span> <span class="variable">$&#123;num1&#125;</span><span class="variable">$&#123;opt&#125;</span><span class="variable">$&#123;num2&#125;</span> | bc )</div><div class="line">     <span class="built_in">echo</span> <span class="variable">$result</span></div><div class="line">     ;;</div><div class="line">     <span class="string">"%"</span>)</div><div class="line">     caculate <span class="variable">$num1</span> <span class="variable">$num2</span> <span class="variable">$opt</span></div><div class="line">     ;;</div><div class="line"><span class="keyword">esac</span></div></pre></td></tr></table></figure>
<p>&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;这个试题遇到的问题就是尽量不要进行变量的复用，变量的多次复用会导致意外的问题。比如从用户那里接受到了 <code>$opt=*</code> ，然后当把变量再赋值给另外的变量的时候那就不是 <em> 了，这个 </em> 会被解析成为当前目录下的所有文件，就会出问题，除非要求用户输入的时候指定  <code>\*</code> 这种格式，给 * 脱意。</p>

	

	
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